1. Field of the Invention
The present invention relates to recording sheets for recording information using ink, or the like. In particular, the present invention relates to recording sheets for use with inkjet printers.
2. Description of the Related Art
Various types of printers are known for use with computers and word processors including dot matrix printers, thermal coloring printers, thermal wax printers, thermal dye sublimation printers, electrophotographic printers, and inkjet printers.
Among these printing methods, inkjet printing is known to have advantages over the other printing methods such as low printing costs, less printing noises, compactness of the printers, and fast printing speeds, and its applications have increased in recent years.
Various types of recording sheets have been proposed for use in the inkjet printing.
One example of the recording sheet for inkjet printing is denoted by reference numeral 110 in FIG. 3a. 
The recording sheet 110 includes a transparent base sheet 111, an ink-receiving layer 112 formed on the base sheet 111, and an ink permeable layer 113 formed on the ink-receiving layer 112.
When an image is inkjet-printed on the recording sheet 110, ink 114 is injected from a nozzle of an inkjet printer onto a surface of the ink permeable layer 113 (i.e., printing surface) (FIG. 3a).
The ink permeable layer 113 includes a filler and a binder and thus has a porous structure formed by the filler particles and the binder. Accordingly, the ink 114, upon striking the surface of the ink permeable layer 113, penetrates into the ink permeable layer 113 in directions perpendicular to the surface of the ink permeable layer through the pores of the porous structure and is absorbed by the ink-receiving layer 112 where it is fixed.
The ink 114 fixed in the ink-receiving layer 112 is observed as dots 117 when viewed from the side of the transparent base sheet 111 that does not have the ink-receiving layer 112. The dots 117 as a whole can be observed as a printed image (FIG. 3b).
Recording sheets such as the above-described recording sheet 110 are widely used in recent years in applications including over-head projectors and electric light-illuminated advertisements.
Aqueous ink is generally used in the inkjet printing. Accordingly, when the ink permeable layer 113 is highly hydrophilic, the ink 114, upon striking the surface of the ink permeable layer 113, may be absorbed in directions parallel to the surface of the ink permeable layer 113 in addition to the direction perpendicular to the surface of the ink permeable layer 113.
In such cases, the amount of the ink 114 absorbed in the direction perpendicular to the surface of the ink permeable layer 113, that is, the amount of the ink 114 absorbed by the ink-receiving layer 112, is reduced. This results in a reduced color density of the dot 117 when the dot 117 is observed from the side of the base sheet 111 that does not have the ink-receiving layer 112.
Moreover, when a significant amount of the ink 114 is absorbed in directions parallel to the surface of the ink permeable layer 113, the ink 114 within the ink permeable layer 113 may overlap with each other. These overlaps may be observed as bleeds in printed images.
A type of recording sheet that has alleviated the above-mentioned problems of the conventional recording sheets is known. Such recording sheets include a porous ink permeable layer to which surfactants have been added (Japanese Patent Laid-Open Publication No. Sho 62-280068). In these recording sheets, the surfactants make the ink permeable layer more lipophilic and less hydrophilic, reducing the affinity of the ink permeable layer for the aqueous ink. This suppresses the dispersion as well as fixation of the ink within the ink permeable layer.
In general, various organic solvents are added to the ink (such as, aqueous ink) for inkjet printing in order to prevent nozzles of the inkjet printers from clogging or in order to facilitate penetration of the ink into the recording sheets. Examples of such organic solvents include polyols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, and glycerol; alkyl ether derivatives of polyols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol monomethyl ether; ester derivatives of polyols such as ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, glyceryl monoacetate, and glyceryl diacetate; water-soluble amines such as monoethanolamine, diethanolamine, triethanolamine, and polyoxyethylene amine; and nitrogen-containing cyclic compounds such as 2-pyrrolidone, and N-methyl-2-pyrrolidone. When the ink containing these organic solvents is applied to the ink permeable layer with a high lipophilicity, the organic solvents in the ink may be dispersed along with coloring components of the ink before the ink permeates through the ink permeable layer.
In one aspect, the present invention provides a recording sheet comprising an ink-receiving layer and an ink permeable layer arranged on a surface of the ink-receiving layer, the ink permeable layer including a filler, a surfactant, and a binder, wherein the surfactant includes a fluorosurfactant having a perfluoro-alkyl group in its chemical structure, and wherein the binder containing as a primary component a water-insoluble resin having a high hydroxyl value of 4 or higher.
In one embodiment of the present invention, the filler may be silica.
In one embodiment of the present invention, the binder may include one or both of the high hydroxyl value resin that is composed of a polyester and the high hydroxyl value resin that is composed of polyvinyl acetal.
In one embodiment of the present invention, the surfactant may be added to the ink permeable layer in an amount of 1 to 30 weight parts with respect to the total weight of the binder and the filler as 100 weight parts.
In one embodiment of the present invention, the binder comprises at least one high hydroxyl value resin selected from the group consisting of polyethylene, polystyrene, polymethacrylate, elastomers, ethylene-vinyl acetate copolymer, styrene-acryl copolymer, polyacryl, polyvinyl ether, polyamide, polyolefin, polysilicone, guanamine, polytetrafluoroethylene, urea resin, phenoxy resin, epoxy resin, and styrene-butadiene rubber.
In one embodiment of the present invention, the filler comprises at least one compound selected from the group consisting of silica, talc, kaolin, clay, zinc oxide, tin oxide, aluminum oxide, calcium carbonate, titanium white, barium sulfate, titanium dioxide, aluminum silicate, magnesium silicate, magnesium oxide, smectite, zeolite, and diatomite.
In one embodiment of the present invention, the recording sheet further comprising a base sheet disposed proximate to the ink receiving layer.
In one embodiment of the present invention, the base sheet comprises at least one compound selected from the group of polyethylene terephthalate, polyesters as polyethylene naphthalate, polyolefins as polyethylene and polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polycarbonate, transparent paper, cellulose acetate, polyacrylate, and polyether sulfone.